As a thiadiazabicyclononate-type agricultural chemical, a compound which has a structure of the following formula: ##STR2## and which is used as an active substance for a herbicide, is, for example, known (see Japanese Unexamined Patent Publication No. 264489/1988). The compound of this formula (2) (hereinafter represented also as the compound (2), the same applies to other compounds) is produced by using 5-amino-2-chloro-4-fluoro-thiophenol represented by the formula (3) (see U.S. Pat. No. 4,613,675) as the starting material: ##STR3##
Heretofore, as a method for obtaining the above compound (3), the following method is known which is a combination of the methods disclosed in Japanese Unexamined Patent Publications No. 172958/1985 and No. 33148/1987: ##STR4##
However, the above conventional method had problems with respect to the safety and toxicity, etc. such that it was necessary to use fumming sulfuric acid containing 60% of SO.sub.3 which was not easy to use for industrial operation, and besides, phosgene was generated during the reaction using carbon tetrachloride as a solvent. Further, for the reduction of the chlorosulfonyl group, a large amount of a reducing agent as well as an excess amount of an acid was required to be used. Therefore, such a method was not satisfactory as an industrial method.
On the other hand, as a method for obtaining the above compound (3), the following method is also known involving a disulfide compound as an intermediate (see Unexamined Patent Publication No. 221254/1990). ##STR5##
However, in the above method, the diazotization operation is cumbersome. Besides, the yield is low, a side reaction proceeds mainly in the nitration, and the yield is also low. Thus, using the disulfide compound as an intermediate does not provide good results, and this method can not necessarily be regarded as a good method.
The present invention has been made for a purpose of overcoming the above mentioned difficulties of the prior art and to provide a novel disulfide compound which can readily be led to the 5-amino-2-chloro-4-fluoro-thiophenol of the above formula (3) in good yield.